The invention relates to conveyors in general, and more particularly to improvements in conveyors which can be utilized to advance successive stacks of superimposed sheets toward a discharging or evacuating station where the stacks come to a halt as a result of impingement upon a suitable abutment or barrier. The apparatus of the present invention can be utilized with advantage to supply stacks of superimposed paper, cardboard, metallic and/or plastic foil blanks to or to transport such stacks in a packing machine wherein successive arrays of plain or filter cigarettes or other smokers' products are confined in envelopes (converted blanks) to form so-called packets ready to be confined in cartons or other suitable receptacles.
A drawback of presently known roller conveyors for the transport of stacks of superimposed sheets of paper or the like is that the lowermost sheets (and frequently one or more sheets above the lowermost sheets) are likely to become shifted relative to the remaining sheets which are located above the lowermost sheet or sheets during advancement of stacks toward a location where the stacks are to be transferred into or are already located at the singularizing station.
Certain types of roller conveyors employ driven shafts which are disposed below the path for the stacks and are loosely surrounded by annular rollers which do or can receive torque from the respective shafts by friction and transmit motion to the lowermost sheets of the stacks. A shifting of the lowermost sheet(s) of a stack relative to the sheets above the lowermost sheet(s) is attributable, at least in part, to the tendency of leading edges of the sheets to bend or curl downwardly and to thus strike against the peripheral surfaces of the rollers which loosely surround the respective driven shafts. The result is a rearward shifting of the lowermost sheets relative to the sheets above them so that the stacks arriving at and impinging upon the abutment include upper regions or strata with accurately overlapping sheets and lower regions consisting of one or more sheets which lag behind (i.e., which have been shifted relative to) the sheets in the respective upper strata. Otherwise stated, the stacks which come to a halt at the discharge end of the roller conveyor normally include sheets (the upper sheets) which come to a halt in optimum positions for singularization and/or other processing, and one, two or even more lowermost sheets which are shifted relative to and lag behind the bulk of sheets above them. This can cause serious problems during further processing, e.g., when the sheets of the stacks are blanks ready to be converted into envelopes for arrays of plain or filter cigarettes, cigarillos or other smokers' products. The same holds true when the sheets of successive stacks are to be utilized in other fields, e.g., for the confinement of reams of paper sheets, for the confinement of foodstuffs or elsewhere.